Anti-reflection films are generally provided on the surface of optical products and the like, for suppression of reflectance based on the principle of optical interference, in order to prohibit reduction in contrast owing to reflection of external light, and also to prevent the display surface from mirroring the surrounding scene. Particularly in such image display devices as a cathode-ray tube display device (CRT), a plasma display panel (PDP), and a liquid crystal display device (LCD), each of which requires that a display image be clearly viewed, the anti-reflection film is arranged at the outermost surface of the display.
Such anti-reflection films can be formed by laminating plural transparent thin layers, which are different in refractivity, and multi-layered films, in which transparent metal oxide thin films are laminated, have been ordinarily used.
Such transparent metal oxide thin films are formed by a chemical vapor deposition (CVD) process or a physical vapor deposition (PVD) process, and particularly by a vacuum vapor deposition process, which is a physical vapor deposition process. These transparent metal oxide thin films have excellent optical characteristics as an anti-reflection film. However, the method of forming a transparent metal oxide thin film by such vapor deposition is insufficient from the standpoint of productivity for mass production.
In place of the vapor deposition process, from the standpoint of mass production, it has been proposed to form anti-reflection films by applying a coating composition containing inorganic fine particles.
For example, JP-A-8-110401 (“JP-A” means unexamined published Japanese patent application) and JP-A-8-179123 disclose a technique that forms a high-refractive-index layer, having a refractive index of 1.80 or more, by incorporating inorganic fine particles having a high refractive index into a plastic, and then applies the high-refractive-index layer to an anti-reflection film. To form a transparent film as a high-refractive-index layer by coating inorganic fine particles, it is necessary to make the particles sufficiently fine and to disperse the particles uniformly in the layer. To disperse the inorganic particles, it has been known to use surfactants or anionic or cationic polymers for dispersion. However, these compounds cannot form bonds with the crosslinked film, after dispersion, and there is a problem that these compounds deteriorate physical strength and chemical resistance of the film.
On the other hand, U.S. Pat. No. 6,210,858, U.S. Pat. No. 6,383,559, JP-A-2001-166104, and JP-A-2001-188104 each disclose an anti-reflection film having, as a high-refractive-index layer, a film containing therein inorganic fine particles dispersed with a crosslinked polymer having an anionic group. Each publication describes an example that the polymer in the high-refractive-index layer is formed by a polymerization reaction of multifunctional monomers, simultaneously with coating the monomers or after coating the monomers. The anti-reflection films have such excellent properties as (1) high productivity at low price, (2) a high-refractive-index layer having a very high refractive index and transparency, and (3) excellent scratch resistance.
By intensive studies on the above-said anti-reflection films, the present inventors revealed a problem that the film mechanical strength was easily lowered by a saponification processing necessary to put an anti-reflection film on a polarization plate. From analysis by the present inventors, it was also revealed that this was caused by penetration of a saponificating liquid into a portion at which a crosslinking reaction was not sufficiently occurred, and by elution of a monomer component that was not completely hardened.